In the manufacture of hydraulic machine runners for turbines, it is known to bolt the runner blades of the turbine onto the runner hub of the turbine with fitted studs and nuts. Typically the hub is hollow and has an outer surface that is conical, cylindrical or spherical in shape. The blade is provided with a circular shaped flange which is bolted to the outer surface of the runner hub by a series of studs and nuts arranged in a single circle that pass through the runner hub and into the flange or trunnion of the runner blade. The bolted connection has the advantages that it allows for an easy adjustment of the blade angle to meet homology requirements during the assembly of the hydraulic turbine, it reduces runner size for transportation and it reduces welding requirements during manufacturing process.
In some hydraulic turbine assemblies, space limitations within the runner hub prevent a sufficient number of bolting connections, arranged in the circular pattern, to pass through the hub and into the circular flange. As a result, in some applications it may not be possible to ensure proper fatigue life of the bolting by flange pre-loading. Further, when the space limitations result in the flange having a smaller diameter than desired, stress levels in the flange can rise over acceptable limits. In these instances the runners are usually assembled without the use of bolting and by welding the runner blades to the runner hub or with the use of segmented casting that is united with shrink rings or welding. However the assembly by welding or segmented casting does not lend itself readily to use in hydraulic turbines which cannot be completely manufactured in a plant due to their size and shipping considerations. In many instances, the hydraulic turbine must be shipped in sections and assembled at site. This is due to the fact that bridge clearances, tunnel sizes, track spacing and other factors all operate to limit the size of articles which can be shipped over any given route. Clearly, the bolted connection of the runner blade to the runner hub is a desirable method of assembling hydraulic turbines that are capable of being pre-assembled in a manufacturing plant, disassembled for shipment and reassembled at the site. Any improvements in this connection would be desirable.